Electrodynamic pickup



Feb. 20, 1951 D. F. BALMER 2,542,457

ELECTRODYNAMIC PICKUP Filed Dec. 51, 1946 2 Sheets-Sheet l VIIIIIIIIIIINVENTOR. DONHL D F. BFIL ME R HTTORNEY Feb. 20, 1951 D. F. BALMERELECTRODYNAMIC PICKUP 2 Sheets-Sheet 2 Filed Dec. 51, 1946 INVENTOR.DONALD E BFILMER FITTORNEY Patented Feb. 20, 1951.

ELECTRODYNAMIC PICKUP Donald F. Balmer, New Haven, Conn., assignor toThe Soundscriber Corporation, New Haven, Conn, a corporation ofConnecticut Application December 31, 1946, Serial No. 719,381 9 Claims.(01. Fill-100.41)

This invention relates to phonographs, and more particularly to anelectrodynamic moving coil pickup located in a. magnetic field and'especially adapted for use on a rotating fiat disk record.

One object of the present invention is to provide an improvedmoving-coil pickup of the above nature having an elongated iron coresurrounded by a similar-shaped coil mounted in a rigid light weightplastic stylus-carrying armature freely and flexibly supported in anintegral soft rubber base in such a manner as to reduce undesiredvertical oscillations of the pickup stylus, and thus avoid resultantgurgling sounds which might otherwise occur.

A further object is to provide a pickup unit of the above nature havinga unitary rubber armature mounting having a stylus-receiving aperture ofwedge-shaped cross section to limit and dampen the lateral vibrations ofsaid stylus.

A further object is to provide a pickup unit of the above nature havinga flat base on which are four upstanding corner lugs for locating andholding the field magnet rigidly in operating position.

A further object is to provide an improved pickup of the above nature,which will be inexpensive to manufacture, freely movable, simple inconstruction, having reduced record wear, compact, improved tracking,low surface noise, ornamental in appearance, faithful in reproduction,and very efilcient and durable in use.

With these and other objects in view, there has been illustrated on theaccompanying drawings one form in which the invention may convenientlybe embodied in practice.

In the drawings,

Fig. 1 represents a side view of the pickup head as it appears duringuse mounted on a supporting arm, and with its stylus resting upon a diskrecord.

Fig. 2 is a side view of the pickup head, shown on a larger scale, andwith the cover casing removed to illustrate the interior construction.

Fig. 3 is a top plan view of the same.

Fig. 4 is a transverse sectional view of the same, taken along the line4-4 of Fig. 3, looking in the direction of the arrows.

Fig. 5 is a longitudinal sectional view of the same, taken along theline 5--5 of Fig. 3.

Fig. 6 is a similar longitudinal sectional view, taken along the line6-6 of Fig. 3.

Fig. 'l is a transverse sectional view, taken along the line 1-1 ofFigs. 3 and 5.

.Stone, October 10, 1944, entitled Stylus Brace for Stepback Mechanisms,and a prior application, Serial Number 548,583, filed August 8, 1944, byDonald F. Balmer, entitled Humless Electrodynamic Pickup, Patent No.2,416,082, dated February 18, 1947.

Referring now to the drawings, in which like reference numerals denotecorresponding parts throughout the several views, the numeral I0indicates a U-shaped magnet having a rear section provided with beveledcorners Ha, Nb, and a pair of forward integral pole pieces I2, l3,having bevelled corners 4, 5, similar to the corners Ha, llb, previouslymentioned.

The forward part of the magnet I0 is provided with a key hole shapedaperture I6 having a round-cornered square rear section IQ for embracingthe rear mounting of the armature 20,

to be described later, said square section being located substantiallyat the center of said magnet I0.

. The forward portion of the keyhole aperture l6 has a pair of inwardlyconverging pole faces l1, l8 for concentrating the magnetic flux on alight-weight non-magnetic U-shaped armature frame 20 preferably of rigidplastic material and having a lower base section 2|.

The armature frame 20 comprises an upstanding front lug 22 provided witha bottom-opening mature 20 is an elongated iron core 26, provided withrounded ends, having three vertical holes 21, and a surroundin elongatedcoil 28 preferably of enameled insulated copper wire. Provision is alsomade of a pair of upstanding short guide pins 25a, 25b-fitted into thefront and rear holes 21.

The armature frame 20 is adapted to be mounted in a-unitary soft rubberU-shaped supporting block 29 havin upstanding integral end posts 29a,2912, provided with dove-tailed diverging ends.

The posts 29a, 29b of the armature supporting block 29 are provided witha pair of integral horizontal pin-receiving sockets 30, 3|, and the baseof said support 29 has a rectangular opening 290, the sides of which arewedge-shaped in cross-section for engaging the pickup stylus 2Ib forlimiting and dampening the vibrations thereof. The wedge-shaped sidesare so constructed that the limiting force will increase more rapidlythan the lateral excursions of the stylus 211), i. e. in accordance witha non-linear function thereof.

One advantage of this construction is that when the pickup is backspacedin transcribing, the use of a stylus brace to prevent undue yielding ofthe armature unit is avoidedthe wedgeshaped edges of the rectangularopening in the rubber mounting serving to limit movements of thearmature to a small angle.

The rubber upporting block is also provided with a pair of longitudinalside grooves 32, 33 for embracing the side edges of a rectangular slot34 in the forward part of a non-magnetic base plate 35.

The base plate 35 has a pair of upstanding hollow arms 3B, 31 providedwith interior dovetail recesses 38, 39, which are adapted to receive andreinforce the upstanding dovetailed legs of the rubber armature support29.

The corners of the base plate 35 are provided with upstandingmagnet-locating pins 42, 43, 44, 45, which are connected to said magnetby anchors 45, 41, d8, 49 of cement, for rigidly securing said pins tothe bevelled corners I la, Nb, :4, and [5 of the magnet H].

The base plate 35 is also provided with a pair of depressed longitudinalgrooves 40, 4| for embracing a pair of lead wires L and L1.

The playback head is also provided with a rectangular nut plate 50 forholding the magnet l firmly upon the base plate 35. The nut plate 50 hasa pair of inwardly-extending inclined fingers for resiliently engaging avertical screw 5| having a head 52 located under the base plate 35.

The pickup head is also provided with a Z- shaped forward handle 54secured to the base plate 35 by screws 54a for facilitating the liftinof the same from the record R located on the, turntable T. A casingcover 53'is secured in position by an ornamental cup-shaped nut 51 onthe top of the screw 5 l.

Provision is also made of a U-shaped terminal guide strip 55 located infront of the magnet [5 for accurately positioning a pair of connectingwires L2, L3, said strip having a pair of side apertures 55a, 55b. Thestrip 55 is connected to the forward post 36 by a pair of rivet pins 55.The casing cover 53 has an upstanding post 58 to which is connected theforward end of a counter-balancing spring 59, the rear end of which issecured to a post 80 on a horizontal pickup arm 6|.

Operation In operation, the lateral vibrations of the pickup stylus Zibin the spiral grooves of the record It will cause the armature 20 tooscillate about a longitudinal axis passing through the small supportingpins 24, 25, with the coil 28 in the field of the magnet pole pieces [7,18. This will produce voltage variations in accordance with themodulations of the speech or other sounds to be reproduced.

While there has been disclosed in this specification one form in whichthe invention may be embodied, it is to be understood that this form isshown for the purpose of illustration only, and that the invention isnot to be limited to a specific disclosure, but may be modified andembodied in various other forms without departing from its spirit. Inshort, the invention includes all the modifications and embodimentscoming within the scope of the following claims.

Having thus fully described the invention, what is claimed as new, andfor which it is desired to secure Letters Patent, is:

'1. lnaphon-ographic electrodynamic pickup, a U-shaped magnet, a rigidcoil-carrying longitudinally-extending armature of non-metallic-material located between the poles of said magnet, a record-engagingstylus depending from said armature, a soft rubber yieldable unitarymounting attached to said magnet and supporting the front and rear endsof said armature, said mounting having a rectangular aperture in itsbase provided with wedge-shaped side edges engaging opposite sides ofsaid stylus to cause the lateral vibrations of said stylus to be opposedby a damping force which increases more rapidly than the excursions ofsaid stylus.

2. In a phonographic electrodynamic pickup, a U-shaped magnet, a narrowrigid coil-enclosing armature of plastic insulating material and havinga record-engaging stylus, said armature comprising a pair of smallhorizontal longitudinal mounting pins at the front and rear endsthereof, a U-shaped cradle mounting comprising front and rear upstandingend posts located between the poles of said magnet, means attaching saidcradle mounting to said magnet, said stylus depending from a forwardportion of said armature and through an opening in said cradle mounting,said end posts having horizontal sockets frictionally embracing saidmounting pins and supporting said armature between said poles, wherebyundesired vertical oscillations of said armature coil may be reduced.

3. The invention as defined in claim 2, in which said attaching meanscomprises a base plate having upstanding reinforcing arms embracingouter surfaces of said end posts.

4. The invention as defined in claim 2, in which said upstanding endposts are dovetailed in'shape, and said attaching means comprises a baseplate having upstanding arms provided with dovetailed recesses receivingsaid end posts, whereby said arms may reinforce said end posts.

5. In a phonographic pick-up comprising a U shaped magnet and a stylusand coil-carrying armature between the poles of said magnet; meansattaching said' armature to said magnet comprising a. base plate, screwmeans clamping said base against an outerisurface of said magnet, aplurality of pins projecting from said base plate outwardly of andadjacent the periphery of said magnet, and cement engaged between saidpins and said magnet, whereby said base plate may be rigidly secured. tosaid magnet and the eifects of possible lateral movements of said screwmeans may be avoided.

6. In a support for a non-magnetic stylus and coil carrying armaturemounted to vibrate between the poles of a U-shaped magnet of aphonographic electrodynamic pickup; a base plate, means for yieldablysupporting said armature on said base plate, and upstanding pinsintegral with said base plate and cemented to the corners of said magnetto securely anchor it in coil carrying armature mounted to vibratebetween the poles of a U-shaped magnet of a phonographic electrodynamicpickup; a base plate, means for yieldably supporting said armature onsaid base plate, upstanding pins integral with said base plate andcemented to the corners of said magnet to securely anchor it in positionthereon, said armature having a flat base provided with a plurality ofupstanding pins, and an elongated iron core fitted over said pins andlocated within said coil.

8. In a phonographic electrodynamic pickup, a U-shaped magnet, anon-magnetic stylus-andcoil-carrying armature mounted to vibrate betweenthe poles of said magnet, a soft rubber yieldable mounting for the frontand rear ends of said armature, said mounting having a pair of parallelwedge-shaped side members engaging said stylus to dampen and limit thelateral excursions thereof.

9. The invention defined in claim 8 in which the dampening force of saidwedge members increases more rapidly than a linear function of saidlateral excursions.

DONALD F. BALMER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,019,052 Lord Oct. 29, 19352,213,936 Thompson Sept. 3, 1940 2,265,840 Hutter Dec. 9, 1941 2,369,676Hunt Feb. 20, 1945 2,382,692 Courcy Aug. 14, 1945 2,410,329 AlbrightOct. 29, 1946 2,412,718 Dally Dec. 17, 1946' 2,416,082 Balmer Feb. 18,1947 2,422,817 Baker June 24, 1947 2,425,567 Robinson Aug. 12, 19472,463,894 Chorpening Nov. 16, 1948 FOREIGN PATENTS Number Country Date350,748 Great Britain June 18, 1931 Certificate of Correction Patent No.2,542,457 February 20, 1951 DONALD F. BALMER It is hereby certified thaterror appears in the printed specification of the above numbered patentrequiring correction as follows:

Column 6, line 22, list of References Cited, under the heading UNITEDSTATES PATENTS, for the patent number 2,463,894 read 2,453,894;

and that the said Letters Patent should be read as corrected above, sothat the same may conform to the record of the case in the PatentOfiice.

Signed and sealed this 29th day of May, A. D. 1951.

THOMAS F. MURPHY,

Assistant Commissioner of Patents.

